This invention relates to a fluid pressure actuated braking system for an articulated vehicle.
Existing braking systems for articulated vehicles, such as the system disclosed in U.S. Pat. No. Re. 25,969, provide both tractor and trailer braking when one of the lines connecting the tractor and trailer braking systems fails. However, in systems of this type, no trailer braking is available in this situation until pressure loss from the failure reduces tractor supply pressure to a relatively low level. When this low pressure level is attained the system applies the trailer emergency brakes, which cannot be released until pressure in the tractor portion of the braking system can be increased.
The system disclosed in the present application detects a failed control line by sensing a pressure differential between the tractor and trailer portions of the service control circuits, whereupon the trailer service line is closed and the trailer supply line is vented to thereby actuate the emergency brakes. Since this pressure differential will be detected before the tractor supply will be depleted to any substantial extent, a higher pressure level will be retained to actuate the tractor service brakes and the emergency brakes on the trailer will be actuated shortly after the pressure differential is detected. Since the emergency brakes will be actuated at substantially the same time that the tractor service brakes are actuated, vehicle stopping ability and stability are improved. Furthermore, upon release of the tractor service brakes, the system automatically resets to charge the trailer supply line to release the trailer emergency brakes.